Measurement of Magnetic Field Distorting the Electron Beam Direction in Scanning Electron Microscope

The magnetic field that is generated by different electric devices in an environment of a scanning electron microscope (SEM) causes the direction of the electron beam to become distorted and, consequently, registered images to become distorted. This paper describes a method for a measurement of the magnetic field affecting the direction of the electron beam. It consists of the analysis of SEM images that are registered for several distances between the final aperture of an electron column and a specimen. Means of the measurement of a constant and a periodic magnetic field are explained. The presented examples show the results of the measurement of the constant field that is generated by coils that are placed either inside or outside the microscope chassis. The results are compared with the ones obtained using a reference magnetometer. In the presented method, a direct magnetic field influence on the electron beam is separated from any other influences. Also, the magnetic field nonuniformity along the electron beam path is considered. The current investigations enable the magnetic field compensation and test the shielding efficiency of the SEM chassis.